Recycling Technology During VOCs Treatment-1

There are many kinds of VOCs(Volatile organic compound), including alkanes, olefins, halogenated hydrocarbons, esters, aldehydes, ketones and aromatic compounds, etc., mainly from pharmaceutical, petrochemical, printing and other industries.

Most VOCs are toxic and will react under light to form photochemical smog. They are one of the precursors of ozone pollution and PM2.5. Long-term exposure to volatile organic compounds will increase the possibility of diseases such as cancer.

In that regard, VOC treatment technology can be divided into two categories: recycling and destruction.

Recycling technology

Adsorption technology

Adsorption method is one of the most widely used VOCs treatment technologies in the industrial application, and is widely accepted. It can be further divided into pressure swing adsorption, temperature swing adsorption, temperature swing - pressure swing adsorption and electric swing adsorption.

Table 1 Comparison of adsorption methods under different process conditions

Activated alumina, silica gel, activated carbon, and zeolite molecular sieves are several common adsorbents on the market.

Compared with zeolite molecular sieves, activated carbon has attracted widespread attention due to its strong adsorption capacity, unique surface structure, and easy regeneration.

Activated carbon comes from a wide range of sources, such as coconut shell, fruit shell, sawdust, coal, asphalt, etc.

Absorption technology

The absorption method uses the principle of similar compatibility between the absorption liquid and the organic waste gas to achieve the purpose of absorbing the organic waste gas.

According to this principle, the absorbent is usually a non-polar or weakly polar liquid with similar properties to volatile organic compounds, and its volatility, environmental protection and economy should also be considered.

Common absorbents can be divided into mineral oils (such as diesel, washing oil and other non-polar mineral oils), water composite absorbents (such as water-washing oil, water-surfactant-auxiliaries and other composite absorbents) and high-boiling organic absorbents. (E.g. DBO, DEHA, DEHP.).

The absorption method has the advantages of mature processing technology, simple equipment and good absorption effect. It can handle most volatile organic compounds and is widely used in industrial fields.

The absorption equipment commonly used in industrial production is packed absorption tower and spray absorption tower. The packed absorption tower has a large phase interface, which can adjust the gas-liquid contact time and gas-liquid ratio in a wide range. At the same time, the operation flexibility is large, the cost is low, and it has good pressure drop and separation efficiency.

Packed absorption tower process flow

Spray absorption tower process flow

Compared with the packed absorption tower, the spray absorption tower has simple structure, low resistance and low investment. As shown in Figure 2, during the absorption process, the absorbing liquid is ejected from the top liquid distribution device and fully contacts with the gas entering at the lower end, which increases the gas-liquid mass transfer area.